1. Field of the Invention
The invention relates to a liquid crystal display and, more particularly, to an image driving system of a liquid crystal display and method for the same.
2. Brief Description of the Related Art
A liquid crystal display (LCD) displays images by applying fluctuating electric field to the liquid crystal to orientate the liquid crystal molecules and thus to modulate the light transmission through the liquid crystal. However, the orientation of the liquid crystal molecules does not simultaneously change with a change of an electric field. Thus, the response speed for displaying an image by a LCD is always lower than that by a typical cathode ray tube (CRT). This causes a serious delay problem when dynamic video images are displayed.
In view of this, a high speed image driving scheme is used to drive a liquid crystal display. The scheme applying higher voltages to each pixel can speed up the response of the liquid crystal molecules, such that the liquid crystal molecules can tilt to preset directions in a frame period.
FIG. 1 is a timing chart schematically shows difference in responses to an applied pixel voltage under an ordinary scheme and a high speed scheme. The horizontal axis represents time, and the vertical axis represents the pixel voltage. Under an ordinary scheme, during a frame period T, the pixel voltage, designated as numeral 1, is changed from V1 to V2, and the transmittance of the pixel that changes as a result of the voltage variation is designated as numeral 2. Comparatively, under a high speed driving scheme, during a frame period T, the pixel voltage, designated as numeral 1′, is changed from V1 to V2′, and the transmittance of the pixel that changes as a result of the voltage variation is designated as numeral 2′. Obviously, the response time based on a high speed scheme is shorter.
The high speed image driving scheme of a liquid crystal display can refer to a U.S. Pat. No. 5,495,265. As shown in FIG. 2, a typical high speed image driving system 10 for a liquid crystal display reads and compares pixel data of a current frame Gn and a previous frame Gn-1, and uses a look-up table to obtain driving values according to the result of the comparisons, and applies the driving values to the pixels to generate a corrected frame Gn′. Apparently, the high speed image driving system 10 needs two memories, one of which is a frame buffer 101 and the other is a mapping table 102.
The frame buffer 101 is used for storing pixel data of a current frame Gn, and outputting pixel data of a previous frame Gn-1. The mapping table 102 is used for storing driving values in correspondence with grayscale values of each pixel datum. Specifically, the mapping table 102 is in a matrix form that records driving values in correspondence with grayscale values of pixel data of the current frame and the previous frame. Typically, the buffer 101 needs to have a capacity capable of storing 24, i.e. 3×8, bits of grayscale values for each RGB pixel data, and the mapping table 102 needs to have a capacity capable of storing 3×28×28 numbers of high speed driving values for each RGB pixel data.
In this way, the high speed driving scheme is heavily loaded with the high cost memory of a liquid crystal display. Furthermore, the high speed driving scheme also causes amplification of the noises on displaying images, and badly influences image quality.